At present, substantially two convertiplane configurations are known: “Tilt Rotor”, in which the semi-wing remain substantially fixed, and only the motor-rotor assemblies rotate relative to the semi-wings; and “Tilt Wing”, in which the rotor attitude is adjusted by rotating the semi-wing and rotors system assembly as a whole.
Examples of “Tilt Rotor” configuration are shown in U.S. Pat. No. 6,220,545 or in US-A-2009/0256026. An example of “Tilt Wing” configuration is shown in EP-A-1057724.
Known tilt-rotor convertiplanes substantially comprise a fuselage, a pair of semi-wings projecting on opposite lateral sides of the fuselage, and a pair of nacelles which rotate relative to respective semi-wings.
Each nacelle houses a relative motor-rotor assembly, which, therefore, rotates together with the nacelle relative to the corresponding semi-wing.
In particular, the semi-wings are straight and each nacelle is arranged substantially at the tip of the relative semi-wings.
Accordingly, the position of nacelles reduces the lifting surfaces of the semi-wings.
A need is felt within the industry to increase the lift acting on the tilt-rotor convertiplane both in the aircraft and in the helicopter mode.
As far as the aeroplane mode is concerned, a need is felt to increase the lifting surface of the convertiplane.
As far as the helicopter mode is concerned, a need is felt to reduce the wing shielding effect during the hovering in the helicopter mode. More precisely, the wind shielding effect is caused by the fact that the downwash of rotor partially impinges on the semi-wings, thus reducing the available lift.
Furthermore, a need is felt within the industry to reduce as far as possible the noise generated by the rotors.
A need is also felt within the industry to highly increase the flexibility of the convertiplane, from several points of view.
In particular, firstly a need is also felt within the industry to maximize the aerodynamic efficiency when the convertiplane is operated predominantly in the aeroplane mode during the mission, and to reduce the weight when the convertiplane is operated predominantly in the helicopter mode during the mission.
Secondly, a need is felt to manufacture a modular convertiplane which may easily switch from an unmanned to a manned configuration.
A need is also felt within the industry to increase as far as possible the stability of the convertiplane, especially during the transition between the helicopter and the airplane mode.
Finally, a need is also felt to reduce the bending moments acting on the semi-wings, due to the presence of the tilting rotors.
US-A-2011/003135 discloses a convertiplane comprising a fuselage, a front wing and a back wing, and a pair of booms extending between wing and each supporting a rotor. Rotors are arranged on lateral sides of fuselage and each rotor tilts in an area defined by the relative side of the fuselage and the front and back wings.
U.S. Pat. No. 6,434,768 discloses a convertiplane comprising a wing and a pair of counter-rotating rotors which may tilt relative to wing. Counter-rotating rotors are coaxially mounted and, therefore, both rotate and tilt about the same axis.